Group:
systems
Topic:
backtracking
Topic:
computer as state machine
Topic:
discrete vs. continuous
Topic:
events
Topic:
Newtonian physics
Topic:
state machine
Topic:
temporal relationships
Topic:
Turing machine
Topic:
what is a number
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Summary
A state is an abstract identifier for an object's current condition. It is like a unitless number without a successor. It can be identified as the current value of an attribute of the object.
For abstract objects, a state is part of the object's description. Typically states are mutually exclusive and the transition between states is instantaneous. For example, there are three components of a Turing machine's total state or configuration: the position of the tape, the current symbol, and the current state.
For natural objects, the state may be ambiguous. Holt illustrates states and transitions between states (i.e., events) by a person crossing a series of mountain ridges. There are two states: on top of a ridge and in a valley. At some times one of these states clearly holds. At other times no state clearly holds. Identifying the state of an object may change that object.
A state may be a function of other states, e.g., a function of the object's attributes.
If a state is a function of prior input, then the state encodes a subset of the possible input histories. It is easy to confuse a state with the functions or input that effects the state. This may be why callback programming can be difficult to learn. (cbb 4/94)
Subtopic: what is state 
| Quote: an automaton's operation is determined by finite, internal states; i.e., stable states of the machine at discrete time intervals; nothing else matters [»rabiMO4_1959]
| | Quote: a state has substance (what has materialized), properties (what is measured), and actions (what is going on) [»nygaK10_1983, OK]
| | Quote: an operation card sets the mill into a specific state in which it will operate on one pair of numbers [»menaLF10_1842, OK]
| | Quote: a universe comes into being when a space is severed [»browGS_1972]
| | Quote: a state in a state machine is a unitless number [»cbb_1980, OK]
| | Quote: defined modes for the system; each mode corresponds to a set of true conditions [»heniKL1_1980]
| | Quote: the state of an AST system is a set of definition rules for determining transitions
| | Quote: the state of a neuron net consists of the afferent stimulation and the activity of each neuron
| | Quote: every substance expresses the universe; its present state contains its past states and all those to come [»leibGW_1686c]
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Subtopic: state as transitive value
| Quote: the state, or value, of an object is the value of its members and the objects it references [»stroB_1991]
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Subtopic: state as abstraction
| Quote: representing prior stimuli by state data (invented abstractions) specifies an implementation
| | Quote: introduce the intermediate state, 'hungry', to solve the dining philosophers problem
| | QuoteRef: wulfWA6_1976 ;;19 Alphard defines abstract states (eg empty stack) for describing different predicates
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Subtopic: state as attributes
| Quote: state-machine paradigm represents state by values of storage variables; must handle simultaneous assignment [»floyRW8_1979]
| | Quote: the state of an object is its internal properties and attributes at a given point in time [»maclBJ12_1982]
| | Quote: a logical expression in TOPD compares a variable (e.g., CH) with a state identifier (e.g., BLANK) [»hendP9_1975]
| | Quote: a state is a predicate representing a property of a system; may have duration
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Subtopic: state vs. transition
| Quote: being in a state is being within a bounded region, while being in a transition is crossing a boundary [»holtAW11_1980]
| | Quote: an object can only be clearly in one state at a time or one transition at a time [»holtAW11_1980]
| | Quote: for atomic objects, a transition can have only one pre-state and post-state while states can have multiple pre/post-transitions [»holtAW11_1980]
| | Quote: the event <9 o'clock> ends the holding of the condition <8 o'clock> and begins the condition <9 o'clock> [»holtAW_1970]
| | Quote: software milestones are the transitions between states as in MONSTR
| | Quote: the greater the INTERESTS of an ORGANIZATION the sharper the boundaries [»holtAW_1997]
| | Quote: navigators distinguish open water and a harbor but not being in between the two; it does not matter
| | Note: a state is a location in a program, i.e., a transition; avoids a circular definition from storing the state [»cbb_1990, OK]
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Subtopic: program flow vs. object state
| Quote: when coding a statement, the programmer must recall program states and evaluate the changes for multiple cases [»snelJL7_1997]
| | Quote: an object's methods interact indirectly through its state variables [»edwaSH2_1997]
| | Quote: many students confuse an object's state with mechanisms that affect that state
| | Quote: callback-based programming was difficult to teach through SUIT; accustomed to using program flow to encode state [»pausR10_1992]
| | Quote: an actor is either active (receiving messages) or idle; can only learn about an undisturbed state by acting on it, active state is inaccessible [»mantMJ2_1983]
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Subtopic: state as separate functions
| Quote: use separate functions instead of a state variable; e.g., 6-60x speedup for binary semaphores [»maurPM3_2004]
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Subtopic: avoid states
| Quote: MacPaint is concrete: the only data structure is bits on the screen, and the user's sole goal is to turn those bits on and off; literally no state to remember [»myerBA_1992]
| | Quote: no side effects to spreadsheet formulas. In general, want to minimize side effects, provide clear cause-and-effect relations, and trace/debug the results [»myerBA_1992]
| | Quote: REST interactions are stateless; they transfer representations of identified resources
| Quote: in paper solutions, participants used future and past tense instead of state variables; but most programming languages require state variables
[»paneJF2_2001]
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Related Topics
Group: systems (17 topics, 530 quotes)
Topic: backtracking (30 items)
Topic: computer as state machine (20 items)
Topic: discrete vs. continuous (47 items)
Topic: events (44 items)
Topic: Newtonian physics (79 items)
Topic: state machine (67 items)
Topic: temporal relationships (40 items)
Topic: Turing machine (30 items)
Topic: what is a number
(55 items)
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